Many machines and equipment circulate fluids that perform various functions such as lubricating moving parts, transferring heat, separating moving parts, absorbing contaminants, and powering hydraulic motors and hydraulic cylinders. Such fluids may include engine oil, transmission fluid, hydraulic fluid, and coolant fluid. For instance, engine oil and transmission fluid may lubricate moving parts such as gears and pistons, while hydraulic fluid may power hydraulic cylinders, such as those used to raise and lower an implement of an earth-moving machine. However, as the machine operates and with extended hours of machine operation, such fluids may degrade due to oxidation, thermal breakdown, and/or contamination. For example, as an engine oil degrades, the acidity of the oil may increase, leading to an increase in the viscosity of the oil and eventual formation of sludge and varnish. When the acid content of the engine oil reaches a certain level, it may signify that the engine oil has reached its useable life and needs to be replaced with fresh oil.
The machine or equipment may also include one or more filters that collect contaminants such as particles and debris that have accumulated in the fluids to protect bearing surfaces, engine liners, and/or other engine parts from wear. Although such filters may extend the period of service of the fluid, they may not be equipped to detect when the fluid has reached its useable life and needs to be replaced.
U.S. Pat. No. 7,043,402 discloses a sensing system for real-time monitoring of the quality of engine lubricating oil. In particular, the sensing system includes at least two electrodes installed on a port of a lubricating oil reservoir that monitor the quality of the lubricating oil based on impedance measurements. Other sensing systems for monitoring machine fluid quality may be complex and/or expensive to implement.
Thus, there is a need for improved sensing systems for detecting degradation of machine fluids.